July 4, 2013

Astronomers Catch Distant Galaxy Snacking On Gas

Astronomers were recently able to catch a distant galaxy in the act of snacking on nearby gas while using the European Southern Observatory's (ESO) Very Large Telescope (VLT).

The team wrote in the journal Science about how they were able to make the best direct observational evidence so far supporting the theory that galaxies pull in and devour nearby material to grow and form stars. Scientists have always suspected galaxies grow this way, but until now, no one has directly observed this act.

Astronomers using VLT studied a very rare alignment between a distant galaxy and an even more distant quasar. The light from the quasar passed through the material around the foreground galaxy before reaching Earth, allowing the team to observe the galaxy and its surrounding gas in more detail.

"This kind of alignment is very rare and it has allowed us to make unique observations," explained Nicolas Bouche of the Research Institute in Astrophysics and Planetology (IRAP) in Toulouse, France, lead author of the new paper. "We were able to use ESO's Very Large Telescope to peer at both the galaxy itself and its surrounding gas. This meant we could attack an important problem in galaxy formation: how do galaxies grow and feed star formation?"

Like a car making a long road trip, galaxies quickly deplete their gas reservoirs as they create new stars. Astronomers assumed from this that galaxies replenished themselves by consuming surrounding gas using its own gravitational pull. As a galaxy drags gas inwards, the gas rotates around the galaxy before falling in. The new observation shows both how the galaxy was rotating and the composition and motion of the gas outside the galaxy.

"The properties of this vast volume of surrounding gas were exactly what we would expect to find if the cold gas was being pulled in by the galaxy," said co-author Michael Murphy of Swinburne University of Technology in Melbourne, Australia in a recent statement. "The gas is moving as expected, there is about the expected amount and it also has the right composition to fit the models perfectly. It's like feeding time for lions at the zoo -- this particular galaxy has a voracious appetite, and we've discovered how it feeds itself to grow so quickly."

Astronomers have discovered evidence of material around galaxies in the early Universe, but this is the first time they have been able to show clearly that the material is moving inwards rather than outwards.

"In this case we were lucky that the quasar happened to be in just the right place for its light to pass through the infalling gas. The next generation of extremely large telescopes will enable studies with multiple sightlines per galaxy and provide a much more complete view," said co-author Crystal Martin of the University of California Santa Barbara.

Astronomers reported last October that our own galaxy is apparently slowly consuming the remnants of an ancient star cluster. A team from Yale University said they found the Milky Way was consuming this "light snack" in the southern Galactic sky region.